The present invention relates to a phase signal detecting device, particularly for alternators of motor vehicles.
As is known, in alternators for motor vehicles it is necessary to monitor the current flowing in each winding of the alternator, which hereinafter will also be referred to as "phase signal", to verify the correct operation of the alternator. More in detail, such monitoring is intended to detect the possible breakage of the belt which makes the alternator rotate or other malfunctions of the alternator itself causing respectively a null phase signal or the phase signal exceeding a preset value. More in detail, each phase signal of the alternator is supplied to a rectifier bridge having a branch composed of two diodes per each phase coil, the phase signal being supplied to the intermediate tap between the two diodes, while a battery is connected to the ends of each branch. Accordingly, on the intermediate tap of each branch of the rectifier bridge there is an approximately square wave since when the phase coil is dispensing current, this intermediate tap reaches a voltage higher than the battery and there is direct voltage on the diode connected at the anode, while when the phase coil is not dispensing current (that is the phase coil is absorbing or taking current) this intermediate tap goes under ground voltage. The square wave, usually taken on only one of the three phase branches, is then processed to evaluate the exact operation of the alternator-rectifier bridge system. For this purpose the square wave is filtered to obtain a continuous signal. Currently, two different systems are employed for filtering the signal which is fed to e.g. a comparator to control whether such continous signal is comprised in a preset range. A first system makes use of an RC filter, which is however rather bulky due to the high value of the capacity necessary at the operating frequency of the alternator (generally 1000 to 3000 Hz according to the speed of the alternator, to the number of poles thereof, and to its type). As a consequence of the dimensions of the filter capacitor, the latter cannot be integrated, so that the overall system is rather bulky. A second filtering system, when a partially or fully integrated circuit is desired, instead makes use of digital components, giving a digital delay by means of counters. However, this solution, too, is disadvantageous due to the significant use of semiconductor area for providing the circuit.